(define (sum-consecutive list state)
  (set! state (if (null? state)
               (first list)
               state))
  (if (= (length list) 1)
      (if (= state (first list))
          state
          0)
      (if (= (first list) (second list))
          (+ (first list) (sum-consecutive (rest list) state)) 0)))

(sum-consecutive '(2 2 1 2) null)